The soft stone was sculptured by the
forces of nature
wind, sun, some rain
who shaped the rocks to a smooth and rounded figures.
After a sufficient reserve of raw limestone has been found, the land that covers the limestone is removed with bulldozers and scrapers. If the chalk is close to the surface, an open shelf quarry method can be used. However chances are that it's deeper in the ground, usually an open pit quarry method is used instead. How this works is — holes are drilled into
the rock, explosives are placed inside, and the
rock is blown apart.
Once large chunks of limestone have been quarried, they need to be transported to crushing
machines where they
are pulverized.The first step is primary crushing. Various crushers exist, but the idea is the same: compress the stone with
jaws or a cone, or shatter it through impact.Secondary crushing is done with smaller crushers that work at higher speeds, producing pebbles which are then ground and pulverized.
The next phase, wet grinding, washes away impurities. This part is necessary to make the limestone suitable for writing purposes. Wet grinding is carried out in ball mills — rotating steel drums
with steel balls inside
that pulverize the
chalk in to fine powder.
After grinding, the chalk particles are sifted over vibrating filters to separate the finer particles. The particles are then mixed with water, pushed through a well cut out hole, and cut to the proper length.Finally, the chalk is cured in an oven for
To make white classroom chalk, the manufacturer adds water to form a thick slurry to the consistency of clay. The slurry is thenplaced into and pushed
out of a hole, into long
thin pieces. Cut into
lengths of approximately
62 centimetres,the sticks are placed on a sheet that contains places for five sticks. The sheet is then placed in an oven, where the chalk cures for four days
at 85 degrees Celsius. After it has cured, the sticks are cut down to 8 centimetres in lengths.